It sounds like yours is similar to mine. Slide the mattress to one side. If you don't find an opening to allow you to reach into the area under the bed, slide the mattress the other way.
When you find the opening, use a flashlight to look in there. You will see the water pump, the valve that opens to allow the fresh water tank to drain through one of those tubes you saw below, and hopefully a tube hooked to a 3 way valve that will let you easily pump the pink stuff through your system if you so choose.
Mine also has shut offs for the outside shower. I can winterize the system, close the shut offs for the outside shower, dewinterize the RV, and have a fully functioning water system with the outside shower still winterized.
It is possible that the low point drain valves may be there also, although mine are elsewhere.